Polycarboxydiphenyl sulfones and anhydrides thereof



3,022,320 POLYCOXYDIPHENYL SULFONES AND ANHYDRIDES THEREOF Ovell Francis Bennett, Woodbury, Melvin L. Huber, Iitman, and Robert A. Smiley, Woodbury,'N..l., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware N Drawing. Filed Jan. 13, 1959, Ser. No. 786,445

! 6 Claims. (Cl. 260-6463) The present invention relates to novel polycarboxydiphenyl sulfones and to novel anhydrides thereof. More specifically, the present invention involves novel polycarboxydiphenyl sulfones of the type represented by 1100? icon wherein at least two carboxy groups are substituted on at least one phenyl group in positions ortho to each other and the valuable anhydrides of the said polycarboxydiphenyl sulfones.

Carboxydiphenyl sulfones which have been prepared include bis(2-carboxyphenyl) sulfone, bis(2,4-dicarboxyphenyl) sulfone, and bis(4-carboxyphenyl) sulfone. A recent US. patent (No. 2,673,218) describes the preparation of monoand dicarboxydiphenyl sulfones by the catalytic air oxidation of the corresponding diphenyl sulfone with an alkyl group substituted in the meta or para position of at least one ring. However, none of the teachings of the prior art pertain to diphenyl sulfones having the carboxy substituents on adjacent carbon atoms. In fact, until now, the preparation of such compounds by oxidation of the corresponding alkyl-substituted diphenyl sulfones was thought to be impossible as the following statement in the heretofore mentioned US. patent indicates:

Where two alkyl groups are attached to a single benzene nucleus, no oxidation to any significant extent takes place insofar as either of these alkyl groups are concerned if they are ortho in position to each other.

These novel polycarboxydiphenyl sulfones have a variety of uses in that extensive field wherein aromatic polycarboxylic acids conventionally are employed. For example, polycarboxydiphenyl sulfones are intermediates to valuable polymers, dyes, esterlubes, adhesives, plasticizers, and pharmaceuticals.- In addition, from polycarboxydiphenyl sulfones having carboxy groups ortho to each other may be formed valuableanhydrides, which, owing to their enhanced chemical reactivity, are useful, in addition to the previously mentioned applications, for curing of epoxy resins and in the manufacture of alkyd resins.

Accordingly, an object of the present invention is the synthesis of heretofore unknown polycarboxydiphenyl sulfones. More specifically an object of the invention is the syntheses of polycarboxydiphenyl sulfones wherein at least one phenyl group contains at least two carboxy substituents which are in ortho position to each other and which polycarboxydiphenyl sulfones are valuable chemical intermediates. A further object is the preparation of anhydrides of the said polycarboxydiphenyl sulfones,

'for epoxy resins.

7 amaze Patented Feb. 20, 1062 these anhydrides being particularly'useful as curing agents Additional objects will become apparent as the invention is more fully described.

' We have found that the foregoing objects are achieved when we prepare polycarboxydiphenyl sulfones by oxidizing by nitric acid at an elevated temperature and superatmospheric pressure a diphenyl sulfone bearing on one or both phenyl groups at least two oxidizable nuclear alkyl substituents in ortho position to each other.

In order to more fully describe the invention, reference is now made to the following examples which illustrate the method of preparing the novel polycarboxydiphenyl sulfones. In all cases, parts are by weight unless indicated otherwise.

EXAMPLE 1 Preparation of Bis(3,4-Dicarb0xyphenyl) Sulfone H0O? COOH Into a suitably designed reaction vessel was introduced 104 parts of bis(3,4-dimethylphenyl) sulfone and 478 parts by volume of a 35% aqueous solution of nitric acid (ca. 203 parts of nitric acid per se). The reactor was pressurized to pounds per square inch and heated to 200 C. After a 3-hour reaction period at 200 C. during which time the pressure autogenously rose to 555 pounds per square inch, the reaction vessel was cooled and vented. The reaction mixture was removed from the reaction vessel, cooled, and filtered. The resulting filter cake was washed with cold water, dried, and recrystallized from acetic acid to yield 113 parts of bis(3,4- dicarboxyphenyl) sulfone having a neutral equivalent of 98.5 (calcd. neutral equivalence 98.5). An additional 10 parts of product was obtained by concentrating the acetic acid filtrate. A total conversion of 82% was obtained.

The identification of the product was confirmed by its infrared spectrum, elemental analysis, and by the elemental analysis and saponification equivalent of the tetran-butyl ester. The results are tabulated below.

COOH

. Neutrali- Elemental Analysis 0 H S zation Equivalent CalCd.f0rC1aHmO1uS 48.8 2.6 8.1 98.5 Found 48.6 2.8 8.3 98.5

Saponification Equivalent Caled. for 03211420103 62.1 6.9 154.7 Found 62.0 6.9 156.3

EXAMPLE 2 The following polycarboxydiphenyl sulfones were prepared according to the general procedure outlined in Ex-. ample 1. In all cases, the structures of the compounds were confirmed by their infrared spectra and by elemental thereof, was obtained which had a melting point of 299- analyses. 302 C. and a neutral equivalent of 113.5 versus 110.8

Starting Material Parts Initial Product Per- N.E.

of Pressure Temp. Time cent HNO (p.s.i.ga.) 0.) (hrs) Conv. Name Parts Name Structural Formula Calcd. Found HO C C O OH bis (3,4-di- 16. 4 32 155 150-190 3. 2 biS (3,4-dl- I 65 98. 5 98. 5

methylcarboxyphenyl) phenyl) HOOC -80 COOH sulfone. sult'one.

HO 0 C 3,4,4-tri- 26 53. 8 175 130-180 4 3,4.4'-tri- 57 116. 8 117. 7

methylcarboxydiphenyl diphenyl HOOC SO OOOH sulfone. sulfone,

2,3,4,5-tetra- 50.8 300 140-182 3 2,3',4'.5 C O OH O O OH 50 98. 5 101 methylditetracar- I phenyl boxydi- O O OH sulfone. phenyl S 02 sulfone. I

C O O H In all cases, an aqueous solution of HNO; (35%) was used. Tabulated parts are parts by weight of pure HNOs.

The anhydrides are prepared conventionally from the calculated for the desired anhydride. Elemental analysis corresponding polycarboxydiphenyl sulfones as exempligave the following results: fied by the following examples.

EXAMPLE 3 Perent Peifient Penszent Preparation 0 Bis(3,4-Dicarboxyphenyl) Sulfone Calculated for C15H7O1S 54.1 2. 43 9.66 Dmnhydride Found 54.0 2.65 9.38

II I! Examination of the infrared spectrum confirmed the polycarboxydiphenyl sulfones and their anhydrides are obtainable in good conversions. It will be evident that one or both of the phenyl rings of the alkyl-substituted diphenyl sulfone may bear nuclear substituents that are not easily oxidized. The presence of such substituents does not interfere in the oxidation of the alkyl groups and the resulting product will be similarly substituted. Included in the definition of nonoxidizable substituents are halo, nitro, alkoxy, carboxy, acyloxy, phenyl, and phenyloxy radicals. The positions of the nonoxidizable substituents, with regard to the alkyl groups in the positions herein defined, are not subject to any limitation.

The tetracarboxydiphenyl sulfones bearing on each Percent Percent phenyl group a pair of carboxy groups in ortho posi- C H tion to each other are of particular significance in that Into a suitably designed reaction vessel was introduced 4 parts of bis(3,4-dicarboxyphenyl) sulfone prepared as described in Example 2 and 54 parts of acetic anhydride. The reaction mixture was refluxed for three hours, reduced in volume to about 40% of its original volume by distilling out acetic anhydride, cooled, and precipitated. The product had a melting point of 275-278 C. (sealed capillary) and a neutral equivalent of 88.8 versus 89.6 calculated for the dianhydride. Elemental analysis of the 5 product gave the following results:

55 they may be dehydrated to form dianhydrides. Such digglg tor ONT-16088 anhydrides owing to their high degree of chemical reactivity and high molecular weight are particularly useful for curing of epoxy resins.

Infrared analysis confirmed the presence of a sulfone 6O Additionally, as illustrated in Example 4, anhydridegroup and anhydride linkages. A conversion of 92% acids having an anhydride group and one or more free was obtained. carboxy groups are easily prepared from the herein dew EXAMPLE 4 scribed polycarboxydiphenyl sulfones having, additionally, one or more carboxy groups in positions other than Preparation of 3,4,4'-Tricar xy ph nyl sulfone 6 ortho to each other.

Anhydria'c Owing to their relatively low cost and accessibility, o the methyl-substituted sulfones were employed in all the preparations exemplified. However, polycarboxydiphenyl 1 I sulfones having carboxy groups in the ortho position to CQSO -Q- each other may be prepared from diphenyl sulfones sub- II stituted by any alkyl group oxidizable to a carboxy group. Generally, the alkyl substituents will not contain more Into an open reaction vessel was introduced 2 parts of than ten fiar ato s- 3,4,4'-tricarboxydiphenyl sulfone which subsequently was The stoichiometry of the nitric acid oxidation of methyl heated to 300-325 C. A light tan solid, 1.81 parts substituents on adiphenyl sulfone requires that two moles presence of the anhydride and the sulfone linkages. A I I conversion of 95.5% Was obtained. if so 4 As can be seen from the foregoing examples, the novel of nitric acid be present for each methyl substituent being oxidized. Obviously, as the nitric acid is consumed, the rate of oxidation decreases. Therefore, it is desirable to utilize an excess of nitric acid to overcome this dilution factor. However, if too much nitric acid is present, nitration as well as oxidation occurs. Accordingly, in order to obtain the maximum yield of the desired product, the presence of 2-4 moles of nitric acid per mole of methyl or methylene carbon is preferable. The concentration of the nitric acid in the reaction zone should be between 15 and 50 percent in order to attain the best results. Below that range, the oxidation is undesirably slow and above that range, the formation of byproducts, i.e., nitration products and/or cleavage prod ucts, substantially increases. We have found that very good yields are obtained. by employing 35% nitric acid.

The range of temperature also is quite flexible and depends primarily on the concentration of nitric acid, the specific diaryl sulfone to be oxidized, the desired reaction time, and the desired yield. From the standpoint of economics, reaction rate, and maximum yield, We have found that the most satisfactory temperature is between 110 and 300 C., particularly between 150 and 200 C.

Suificient pressure to maintain a liquid phase must be employed. The specific pressure selected within this limitation is not critical and depends in part on the reaction temperature. Generally, 150 to 200 pounds per square inch gage is satisfactory, and within the range of economical operation.

The polycarboxydiphenyl sulfones and anhydrides prepared in the examples of the present specification have not been previously described in the literature. The novel diphenyl sulfones are characterized by bearing two nuclear carboxy substituents ortho to each other on the same phenyl ring. Additionally, the diphenyl sulfone may have a carboxy group adiacent the sulfone group. As stated previously, additional substituents such as nitro, halo, phenyl, phenyloxy, or alkoxy may be present in any of the free nuclear positions. The new compounds have a plurality of valuable utilities among which are the preparation of novel crosslinked polymers and/or novel hardenable epoxy resin compositions. Esters of the compounds may be formed with alcohols containing 1 to 12 carbon atoms. These esters will find a variety of applications as plasticizers, polymer intermediates, and the like. The use of the esters as plasticizers has been found to impart particularly desirable electrical properties to the compositions into which they are incorporated. The anhydrides of the polycarboxydiphenyl sulfones are of particular commercial significance with respect to the utilities previously discussed for the polyearhoxydiphenyl sulfones in that no by-product water is formed.

The invention has been described in detail in the foregoing, and we intend to be limited only by the following claims.

We claim:

1. As a novel composition of matter, bis(3,4-dicarboxyphenyl) sulfone.

2. As a novel composition of matter, the dianhydride of bis(3,4-dicarboxyphenyl) sulfone.

3. As a novel composition of matter, 3,4,4'-tricarb0xydiphenyl sulfone.

4. As a novel composition of matter, the anhydride of 3,4,4-tricarboxydiphenyl sulfone.

5. As a. novel composition of matter, '2,3,4',5-tetracarboxydiphenyl suifone.

6. As a novel composition of matter, the anhydride of 2,3,4,5-tetracarboxydiphenyl sulfone.

References Cited in the file of this patent UNITED STATES PATENTS 2,614,120 Caldwell Oct. 14, 1952 2,673,218 Caldwell 'Mar. 20, 1954 2,794,822 Schweitzer June 4, 1957 2,895,842 Caldwell et a1. July 21, 1959 

2. AS A NOVEL COMPOSITION OF MATTER, THE DIANHYDRIDE OF BIS-(3,4-DICARBOXYPHENYL) SULFONE. 